1. Field of the Invention
The present invention relates to a rotatable tool and apparatus therefor, and more specifically to a rotatable, linearly moveable tool and apparatus such as an apparatus and device for friction stir spot and/or stitch welding.
2. Description of the Prior Art
Various tools or devices with rotatable tool heads are also linearly moveable, or designed for linear movement, between operative and non-operative positions or between various linear stages of operative positions. Examples include tools and devices for friction stir welding, machining/milling, boring/drilling, routing, screw fastening and lift and rotate operations, among others. Desired characteristics of all such tools and devices is that they exhibit excellent stability and balance and are as linearly compact as possible. Although the present invention has potential applicability to all of the above, it has particular applicability to friction stir welding and more specifically to an apparatus and device for friction stir spot and/or stitch welding. Accordingly, the summary of the invention and the preferred embodiment will be described with respect to an apparatus and device for friction stir spot and/or stitch welding.
Friction stir welding (FSW) is a material joining technique invented by the Welding Institute of England in 1991. The process involves applying a rotating tool or tool head of various configurations to the abutting faces of two or more workpieces, thereby generating frictional heat. The frictional heat in turn creates a softened plasticized region around the immersed rotating tool which is extruded from the leading side to the trailing side of the tool as the tool traverses along the joint. Friction stir welding is attractive for its ability to join various metals including various aluminum alloys, lead, magnesium, steel, titanium, zinc, copper, various metal matrix composites and various other metals often considered as being difficult to weld.
Friction stir welding has been used extensively to perform seam welding either to join two pieces of material together along a lap seam or joint or along a butt seam or joint. More recently, friction stir welding has been applied to spot welds by pressing the rotating head of the FSW tool against the outer surface of two or more layers of material. During the friction stir spot welding process, the rotating head creates friction to plasticize the various layers of material, after which the tool is withdrawn, leaving a spot weld joining the two or more layers of material.
Conventional spot welding involves positioning a pair of electrodes on opposite sides of two or more layers of material and applying sufficient welding energy and pressure to join the layers together. Conventional spot welding is widely used in various industries and applications including the automotive industry. While the use of friction stir spot welding has significant potential applicability for use in the automotive and these various other industries, it also faces several obstacles. These include, among others, the large size and payload of existing FSW equipment and the cost of such equipment as compared to equipment for other conventional joining or spot welding techniques.
Accordingly, there is a need in the art for a compact, low cost friction stir weld device and apparatus which can be used for spot and/or stitch welding applications.